I. Field of the Invention
The present invention relates generally to multi-access communication systems. More specifically, the present invention relates to an apparatus and a method for address assignments for multiple telephone sets in satellite telephone systems.
II. Description of the Related Art
Many communication systems, such as satellite systems, multidrop telephone lines, and multitap bus systems use multi-access communication system configurations. Generally, in a multi-access communication system, a plurality of nodes are connected to a single multi-access channel or an interface bus. Each node has a queue of packets, representing data to be transmitted over or by the interface bus. The interface bus views all waiting packets as one combined queue to be served by an appropriate protocol.
Several methods for access to an interface bus have been developed for multi-access communication systems. One method is the xe2x80x9cfree-for-allxe2x80x9d method in which nodes normally send new packets immediately, hoping for no interference from other nodes. The problem, however, is that packets need to be retransmitted when collisions, that is, interference, occur. The other method is the xe2x80x9cperfectly scheduledxe2x80x9d method in which there is some order in which nodes are allocated reserved time intervals for interface bus access.
Multi-access channels are being considered for interfacing the components of various satellite telephone systems currently under development. For example, multi-access access channels are being considered for providing service for fixed user terminal (UT) systems planned for use in some satellite communication systems. A fixed UT, also called a mobile station, subscriber unit, or a communication terminal, can be a telephone, a wireless unit or a fixed station. The fixed UT is designed to operate from a fixed location. Generally, the fixed UT includes a radio antenna unit (RAU) and one or more telephone sets (also called desksets) connected to the RAU.
A remote location with party line service can be efficiently linked to a satellite or other wireless communications system through a radio antenna unit (RAU). An RAU is a transceiver, comprising well known elements, that transmits and receives a modulated carrier signal to and from the satellite communications systemthrough an antenna. The RAU generally includes a receiver, a transmitter and other signal processing circuitry required for wireless operations. The RAU provides receive and transmit capabilities for one or more telephone sets. During transmission, the RAU accepts audio signals from the multiple phones. An audio coder-decoder (or audio codec) in the RAU digitizes the audio signals, which are then used to modulate the carrier signal that is radiated to a satellite (or other relay apparatus) by the antenna. During reception, the RAU receives an input signal comprising a modulated carrier signal from a satellite. The RAU demodulates the input signal to retrieve the digital audio signal. After which, the audio codec converts the digital audio signal to an analog audio signal, and causes the analog audio signal to be sent to the multiple phones. The RAU can use a variety of additional signal processing and control elements as desired, and known in the art.
There are various advantages associated with the fixed UT. The fixed UT is relatively inexpensive to implement. The fixed UT appears to be especially suitable at remote locations, such as oil rigs, isolated rural areas, and the like where it may not be economically feasible to link such remote areas by land lines.
The fixed UT also appears to be suitable in areas where a typical wireless local loop may not be economically feasible. In a wireless local loop, multiple cellular telephones communicate using a base station (cell site or station). The base station is connected to a public switched telephone network (PSTN) through land lines. However, in some areas, there may not be enough wireless telephone users to justify the installation of a base station. There may also be a lack of sufficient public telephone network infrastructure. For those areas, a fixed UT with a single RAU being serviced by a satellite system or fixed relay stations is a preferred alternative.
The practical implementation of the fixed UT, however, still presents numerous challenges. What is needed is a suitable interface bus (i.e., the multi-access channel) so that the RAU can be connected to multiple desksets. Also, there is a need for a method that will enable the desksets to share the interface bus and to prevent a collision in the interface bus when a plurality of desksets transmit packets simultaneously. Also, there is a need for a method for assigning an address number to each deskset so that it can receive and transmit packets of information.
The present invention is directed to an apparatus and a method for assigning addresses to terminals in fixed UT systems that include a common node, such as a radio antenna unit (RAU), and one or more desksets, such as telephones. The desksets are connected to the RAU through an interface bus.
In one aspect, the method includes the steps of transmitting a request for a first address from one of the terminals to the common node, determining whether or not the first address is in use by any other terminal, transmitting an address grant packet from the common node to the one of the terminals when no other terminal is using the first address, or transmitting an address reject packet from the common node to the one of the terminals when another terminal is already using the first address, and transmitting a request for a second address from the one of the terminals to the common node when an address reject packet is received.
In another aspect, the method includes the steps of transmitting, from one of the plurality of terminals, a request for an address, detecting a collision on the interface bus when another of the plurality of terminals concurrently transmits a request for an address, and retransmitting, from the one of the plurality of terminals, the request for an address after a time-out period has elapsed.